Process for comminuting fluorescent whitening agents and compositions obtained thereby

ABSTRACT

A process for comminuting relatively large crystals of a solid fluorescent whitening agent to a particle size of approximately 5 microns in the largest dimension which comprises grinding either a dry presscake or a water-containing presscake of said agent in admixture with anhydrous sodium sulfate.

United States Patent Langstroth ]*Mar. 11, 1975 PROCESS FOR COMMINUTING[51] Int. Cl D06l 3/12 FLUORESCENT WHITENING AGENTS AND [58] Field OfSearch 252/3013 W COMPOSITIONS OBTAINED THEREBY [75] Inventor: TheodoreA. Langstroth, Cincinnati, [56] References C'ted Ohio UNITED STATESPATENTS 73 Assignee; Sterling Drug Inc New York 3,472,842 l0/l969Hausermann et al. 260/240 B 3,511,833 5/1970 Tscharner 260/240 B Notice:The portion of the term of this Patent q fl to 25/ 1990 PrimaryExaminer-Arthur P. Demers has been dlsclalmed- Attorney, Agent, orFirmLynn T. Fletcher; B. 22 Filed: June 1, 1973 Woodrow Wyatt 211 App].NO.2 366,069 [57] ABSTRACT Related Application Data A process forcomrninuting relatively large crystals of ClmIinuflIiW-in-Pa" 0f201,193, Y- a solid fluorescent whitening agent to a particle size of1971, No. 3,781,215, h c 15 3 approximately" 5 microns in the largestdimension f gf' of 839303 July which comprises grinding either a drypresscake or a 1969 water-containing presscake of said agent inadmixture 52 US. CL... 252/3013 w, 241/30, 252/3012 w, anhydrous Sulfate8 Claims, N0 Drawings 1 PROCESS FOR *COMMINUTING FLUORESCENT WHITENINGAGENTS AND COMPOSITIONS QBTA INED THEREBY This application is acontinuation-in-part of my prior copending US. patent application Ser.No. 201,198, filed Nov. 22, 1971, now U.S. 'Pat. No. 3,781,2l5 which isin turn a continuation-in part ofmy applica' tion Ser. No. 839,703,filed July 7, i969, copending with said application Ser. No. l,l98 andnow abancloned.

This invention relatesto a proccssifor grinding solid particulatematerials and to compositions of matter so obtained. More particularly,theiinvention relates to a process for comminuting solid fluorescentwhitening agents and toarticles of manufacture comprising solidfluorescent whitening agent compositions useful for :in-

corporation into detergents.

Solid detergent compositions today universally contain fluorescentwhitening agents, also called optical bleaches or optical brighteners.In general, the fluorescent whitening agents are amorphous or preferablycrystalline solid organic compounds which are reasonably water-solubleby virtue of the presence in the molecule of one or morewater-solubilizing substituents, for example the sulfonate anion and/oramine substituents. The compounds are ideally white, but in practicethey are generally cream-colored to yellowish'powders, depending uponthe nature of the compound itself, the form in which it exists(amorphous or crystalline, and the nature of the crystalline form) andthe manner in which it is isolated and dried. Furthermore, a number offluorescent whitening agents are rather sensitive to heat. and tend toturn yellow during the drying of the presscakes unless a low temperatureis maintained. Moreover, certain fluorescent whitening agents, forreasons which are not fully understood, tend to turn yellow in colorwhen ground to very fine particle size. The yellow color imparted to thewhitening agents by the above-mentioned processes makes them lessdesirable for incorporation into white detergents because of theyellowish tint which may result in the detergent composition.

It is an object of the present invention to provide an effective methodfor comminuting relatively large crystals of a substantially whitefluorescent whitening agent to an average particle size in the range ofl to 15 microns, but preferably to approximately 5 microns in thelargest dimension without undue yellowing of its color. It is anotherobject of this invention to provide an efficient method for removing theexcess water from presscakes of fluorescent whitening agents withoutsubjecting the fluorescent whitening agent to high drying temperatures.It is yet another object of this invention to provide an effectivemethod for simultaneously drying and grinding a relatively whitefluorescent whitening agent without substantially yellowing the color ofthe product. And it is a further object of this invention to provide anovel fluorescent whitening agent composition consisting offinely-comminuted fluorescent whitening agent and a compatible, inertdiluent in the form ofa free-flowing powder. As used herein, the termrelatively large crystals means crystals substantially larger than fivemicrons and generally in the range of to 100 microns or larger in thelargest dimension.

It has now been found that all the aforementioned objects of the presentinvention can be accomplished 2 by'comminuting thecrystalline'fluorescent whitening agent, eitherin the form ofawater-containing presscake or in theform ofa dry presscake, withanhydrous sodium sulfate. When a watencontaining presscake of thefluorescent whitening agent is to be comminuted,

there is employed as a minimal amount. a sufficient quantity ofanhydrous sodium sulfateto completely interact with the water held bythepresscake. The compositions of this invention prepared fromwatercontaining presscakes thus contain hydrated sodium sulfate. Thecompositions may be utilized as such or may optionally be dried toremove the water ofhydration without undue yellowing of the color o'fthecomposition.

In the first of its process aspects, this invention resides-inaprocessfor'treatingapresscake consisting essentially of water andrelatively large crystals of a fluorescent whitening agent, whichcomprises grinding said presscake at a'temperatureof 20 to 60C in thepresence of at least one and up to eight molecular equivalents ofanhydrous sodium sulfate foreach ten molecular equivalents of water insaid presscake until the crystals are reduced to an average particlesize ofapproximately 5 microns with substantially none of the crystalsgreater than 15 microns in the largest dimension.

In a second process aspect, this invention resides in a process whichcomprises drying the product of the first process aspect above-describedr0 remove some or all of the moisture content.

In a third process aspect, this invention resides in a process fortreating a dried presscake consisting essentially of relatively largecrystals ofa fluorescent whitening agent which comprises grinding saidpresscake in the presence of anhydrous sodium sulfate until the crystalsare reduced to an average particle size of ap proximately 5 microns withsubstantially none of the crystals greater than 15 microns in thelargest dimension.

in one of its composition aspects, the invention resides in an articleof manufacture which comprises a relatively white fluorescent whiteningagent in crystalline solid form having an average particle size ofapproximately 5 microns with substantially none of the crystals greaterthan 15 microns in the largest dimension and, in admixture therewith,crystalline sodium sulfate decahydrate.

In a second of its composition aspects, the invention resides in anarticle of manufacture which comprises a fluorescent whiteningcomposition obtained in accordance with either the second or the thirdprocess aspect of this invention and having a moisture content of lessthan two precent consisting essentially of a crystalline fluorescentwhitening agent having an average particle size of approximately 5microns with substantially none of the crystals greater than 15 micronsin the largest dimension and, in admixture therewith, anhydrous sodiumsulfate.

In a third composition aspect, the invention resides in an article ofmanufacture prepared in accordancev with the first process aspect ofthis invention, which comprises a solid, particulate fluorescentwhitening agent having an average particle size of approximately 5microns with substantially none of the crystals greater than 15 micronsin the largest dimension and, in admixture therewith, crystalline sodiumsulfate decahydrate.

The manner and process of making and using the invention and the bestmode comtemplated by the inventor of carrying out this invention willnow be described so as to enable any person skilled in the art to whichit pertains to make and use the same.

In accordance with the first process aspect of this invention a solid,crystalline fluorescent whitening agent in the form of a presscake,containing essentially only water and the fluorescent whitening agent,is admixed with anhydrous sodium sulfate and the mixture is ground byone or more of a number of grinding processes known to the art. Thequantity of anhydrous sodium sulfate used depends chiefly on the amountof water present in the presscake and the particular activeconcentration of fluorescent whitening agent desired in the finalcomposition. However, there must be used as a minimal quantity at leasta sufficient amount of anhydrous sodium sulfate to interact completelywith the water contained in the presscake for the formation of sodiumsulfate decahydrate (Glaubers Salt). Thus, as a minimal amount, at leastapproximately one molecular equivalent of anhydrous sodium sulfate isused for each ten molecular equivalents of water in the presscake, asdetermined by routine analytical procedures.

Larger amounts of anhydrous sodium sulfate are used in preparing thecompositions of this invention in accord with the first and thirdprocess aspects when it is desired to obtain a particular concentrationor cut of active whitening agent in the composition. With regard .to thecontent of whitening agent, I have found that when compositions in whichthe concentration of fluorescent whitening agent ranges from abouttwenty to about eighty percent are employed in the proper amount toproduce equal concentrations of whitening agent, substantiallyequivalent qualities of whitening effect. solubility and color effect indetergents are obtained. However, for practical use, I prefer to obtaincompositions which have an active fluorescent brightening concentrationin the range of approximately 35 to 70 percent and conversely aconcentration of 65 to 30 percent of the inert non-whitening ingredient.

In accordance with the third process aspect of this invention a solid,crystalline fluorescent whitening agent in the form of a presscake,containing essentially only the fluorescent whitening agent, is admixedwith anhydrous sodium sulfate and the mixture is ground by one or moreof a number of grinding processes known to the art. However, it isdesirable to select a grinding process in which there is provision forcontrolling the temperature of the material being ground in order toprevent excessive heating and thereby causing undue yellowing of thewhitening compositions. I have found in this respect that the grindingoperation carried out on the mixture of dry presscake and anhydroussodium sulfate can be advantageously carried out at temperatures up to100C without undue yellowing. However, I prefer to effect the grindingoperation at a temperature in the range of to 80C. The quantity ofanhydrous sodium sulfate used in accordance with the third processaspect ofthis invention depends on the particular active concentrationof fluorescent whitening agent desired in the final composition.Generally, I prefer to carry out the grinding of the dry presscake inthe presence of approximately to approximately 65 percent of anhydroussodium sulfate by weight of the resultant mixture.

When a water-wet presscake of fluorescent whitening agent is employed inthe processes of this invention, the presscake can have a wide range inthe ratio of solids to water, for example, from about 40 to 80 percentof solids. However, I prefer to use thosewater-wet presscakes in whichthe solid content is in the range of approximately 40 to approximately60 percent ofthe total weight of the wet presscake. When presscakecontaining the preferred proportion of solids (40 to 60 percent) isused, one to eight molecular equivalents of anhydrous sodium sulfate foreach ten molecular equivalents of anhydrous sodium sulfate for each tenmolecular equivalents of water in the presscake is sufficient to obtaincompositions of the invention having the preferred concentrations (35 topercent) ofactive whitening agent specified above.

A more specific embodiment of the first process aspect of this inventioncomprises treating a presscake consisting essentially of water andrelatively large crystals of a fluorescent whitening agent by grindingsaid presscake at a temperature of 20 to 60C in the presence of onemolecular equivalent of anhydrous sodium sulfate for each ten molecularequivalents of water in said presscake until substantially all of saidcrystals are reduced to a diameter of less than approximately 5 microns.Thus, a mixture of approximately one molecular equivalent ofanhydroussodium sulfate per each ten molecular equivalents of water in thepresscake, as determined by routine analytical procedures, is during theinitial stages either heated, or allowed to heat spontaneously, byvirtue of friction and the heat of hydration ofsodium sulfate, to atemperature within the range 35 to 60C (that is, above the melting pointof sodium sulfate dec'ahydrate, 324C), preferably about 50-60C. At thisstage, the mixture becomes a paste or doughlike mass consisting offluorescent whitening agent dispersed in molten sodium sulfatedecahydrate. The mixture is then allowed to cool to approximately 33C(i.e., below the melting point of sodium sulfate decahydrate) and themixture is ground at this temperature for from one-half to 2 hours,depending upon the size of the batch, the original size of the crystalsof fluorescent whitening agent, and the nature of the particularfluorescent whitening agent being processed. The-temperature of themixture is then allowed to fall to room temperature and the resultingdry, free-flowing powder consisting of finely comminuted fluorescentwhitening agent dispersed in crystalline sodium sulfate decahydrate iscollected.

The nature of the grinding apparatus is not critical in carrying out theprocesses of my invention, but for those grinding operations carried outon mixtures prepared from water-wet presscakes, I ordinarily preferapparatus which is capable of exerting a shearing action on therelatively stiff pasty material and thus grinds the fluorescentwhitening agent efficiently in the presence of the sodium sulfate as agrinding aid. An example of an efflcient apparatus for this purpose is adough mixing machine commonly called a flusher fitted either with asigma-type blade or a dispersion blade. The dough mixing machines arecommonly jacketed and can be heated or cooled as desired.

I have also found that a two-roll mill in which the rolls rotate atdifferent rates affords an excellent means of grinding the mixturesprepared from water-wet presscake. Such mills provide the highlydesirable shearing action. Particularly advantageous for grinding thesemixtures are two-roll mills which have rotation ratios in the range of111.1 to 111.25 and which can be made to exert separation forces in therange 1,000 to 2,000 pounds per linear inch.

When a two-roll mill is employed as the grinding apparatus in theprocesses of this invention, the water-wet presscake and the anhydroussodium sulfate are first intimately mixed or blended. The mixing iscarried out in any conventional mixing or blending apparatus such as,for example, a flusher as described above or a ribbon-blender. Themixing is continued only long enough to insure complete blending and themixture is then passed directly on to the two-roll mill. After passingthrough the mill, the composition is either pulverized directly or ifdesired in first dried and then pulverized.

I have found that grinding the mixtures prepared in accordance with thethird process aspect of this invention, that is, those mixtures preparedfrom dry presscake and anhydrous sodium sulfate, it is not necessary toemploy grinding apparatus which exerts a shearing action, but ratherapparatus which effects the gringing by self-impact gives excellentresults. Particularly useful for grinding these compositions are millsgenerally classified in the art of grinding as fluid energy mills. Thereare a number of advantages associated with the use of this type of mill,namely: the mixture being ground is readily held at a relatively lowtemperature during the grinding operation; dusting problems are held toa minimum; and the fluid energy mill permits a continuous grindingoperation.

A more specific embodiment of the third process aspect of this inventioncomprises treating a dry presscake consisting essentially of relativelylarge unground crystals of a fluorescent whitening agent by blendingsaid presscake with a quantity of anhydrous sodium sulfate sufficient toproduce in the resultant mixture a concentration of the fluorecentwhitening agent in the range of approximately 35 to approximately 70percent by weight and a corresponding concentration of anhydrous sodiumsulfate in the range of approximately 65 to 30 percent by weight. Any ofa number of conventional blending techniques and types of apparatus canbe utilized to prepare the mixture prior to the grinding operation. Ihave found that a ribbon-blender is particularly advantageous forpreparing the subject blend. After blending, the dry, free-flowingmixture is passed through a fluid energy mill using for grinding energypre-dried compressed air at approximately. 50C and approximately 90pounds per square inch feed pressure and at approximately 120 pounds persquare inch grinding pressure. The resulting dry, free-flowing powderconsisting of fluorescent whitening agent comminuted to an averageparticle size ofapproximately 5 microns dispersed in sodium sulfate iscollected.

It will be apparent that the compositions of this invention obtained asdescribed above, by converting a watcrwet presscake to a free-flowinggranular powder, retains substantially all the water from the presscake.Thus. when one molecular equivalent of anhydrous sodium sulfate isemployed for each ten molecular equivalents of water in the presscake,the water is present in the final composition in the form of sodiumsulfate decahydrate. For economic considerations and for someapplications it is sometimes desirable to utilize substantially dryfluorescent whitening compositions and in these instances thecompositions of this invention obtained as described above can besubjected to conventional drying techniques known to the art, forexample, oven-drying or flash-drying to remove either some or all of themoisture content with substantially no deleterious effects on the coloror effectiveness of the compositions. l have found that compositions ina state of complete dryness tend to absorb small quanti tits of moisturefrom the atmosphere and equilibrate in a range of approximately /2 to 1/2 percent moisture content. The compositions dried to less than 2percent are particularly preferred because in addition to possessing theexcellent qualities previously noted, they also have excellent storageproperties ordinarily encountered in commercial use.

The new processes of this invention are particularly adapted totreatment of fluorescent whitening agents employed in commericaldetergents and fabric softeners thereby to produce compositions with theimproved characteristics as herein indicated. The following compounds,useful as fluorescent whitening agcnts, are effectively dried andcomminuted by my new process:

Disodium 4,4'-bis(4,6-dianilino-s-triazin-2-ylamino)-2,2-stilbenedisulfonate Disodium4,4'-bis(4-anilino-6-morpholino-s-triazin-Z-ylamino)'2,2-stilbcnedisulfonate Disodium 4,4-bis(4-anilino-6-[2,2-

dihydroxyethylamino]-s-triazin-2-ylamino)-2,2-

stilbenedisulfonate Disodium 4,4-bis(4-anilino-6-[2-hydroxyethylamino]-s-triazin-2-ylamino)-2,2-stilbenedisulfonate Sodium2-(4-stilbyl)-naphtho[1',2:4,5]-l,2,3-

triazole-Z-sulfonate In contrast to the compositions of this invention,flu orescent whitening agents heretofore have been used in commerceeither unground or ground in any of a number of common impact-typemills, for example, a hammer mill. Commercial fluorescent whiteningagents produced by these known processes commonly average 15 microns ormore in their largest dimension. It has also been known to subjectfluorescent whitening agents of the type described herein to comminutionin fluid energy mills. But such attempts have also been found to have aparticle size limitation of approximately 10 microns inthe largestdimension. Efforts to reduce the size of these crystals further haveheretofore yielded a product which is much too yellow in color to havevalue for use in modern detergents.

The composition according to the second composition aspect of theinvention is characterized as a white to yellowish-white free-flowingpowder which is readily soluble or dispersible in water or aqueous soapor synthetic detergent solutions and which has a moisture content ofless than 2 percent. The composition consists essentially ofapproximately 35 to approximately percent by weight of the crystallinefluorescent whitening agent in finely divided form and approximately 65to 30 percent by weight of anhydrous sodium sulfate.

The composition according to the third composition aspect of theinvention contains from approximately 35 to approximately 70 percent byweight of sodium sulfate decahydrate and from approximatley 65 toapproximately 30 percent by weight of dry fluorescent whitening agent isfinely divided form. This composition is characterized as a white toyellowish-white free-flowing powder which is readily soluble ordispersible in water or aqueous soap or synthetic detergent solutions.

The compositions provided by this invention are useful as opticalwhitening and brightening agents, particularly when incorporated intosolid detergent or soap compositions, liquid detergent formulations andtextile softeners. They are also useful for whitening and brighteningtextiles and paper in the absence of detergents in accordance withprocedures well known to the art. A decided advantage of thecompositions of this invention over those of the prior art is the highdegree of water solubility of the fluorescent whitening agent, even incold water. Moreover, more efficient whitening is accomplished by theuse of these compositions because of their improved solubilitycharacteristics over the same compounds obtained in accordance withknown methods.

The following example serves to further illustrate the invention withoutlimiting the latter thereto.

EXAMPLE 1 A l-gallon laboratory flusher (dough mixer), fitted with asigma-type blade and a heating and cooling jacket. was charged with a1035 g presscake of disodium4,4'-bis(4-anilino-6-morpholino-s-triazin-2- ylamino)-2,2'-stilbenedisulfonate containing 73 percent solids [766 g of fluorescentwhitening agent and 260 g (14.9 moles) of water]. Anhydrous sodiumsulfate (206 g; 1.45 moles) was added, while mixing was continuouslymaintained, and then the mixture was heated to 55C. When the mass becamepaste-like, the temperature was lowered to 33C, and the mixing wascontinued for 1 hour. The mixture was then cooled to 28C, whereupon thepaste-like mass solidified and was broken up by the blades into a finegranular powder. There was thus obtained 1,172 g ofproduct whichcontained approximately 65 percent of disodium 4,4-bis(4-anilino-6-morpholino-s-triazin-Z-ylamino)-2,2'-stilbenedisulfonate and approximately 35 percent sodium sulfatedecahydrate. Examination of this product under the microscope showedthat the fluorescent whitening agent existed as broken crystalsaveraging 3 microns with substantially no crystals greater than micronsin the largest dimension.

The rate ofsolution of the above-described composition in water wasdetermined by continuously measuring the fluorescence of a solution ofthe composition in contact with a weighed sample of the product. Thefluorescence was measured on a Turner Fluorometer (G. K. TurnerAssociates, Palo Alto, California). Following are the data obtained,comparing the rate of solution of the above described composition ofthis invention with a standard sample of disodium 4,4'-bis(4-anilino-6'-morpholino-s-triazin-Z-ylamino-2,2'-stilbenedisulfonate dried and groundin the conventional manner. The crystals of the standard sample wereneedles or rods which had been ground in an impact-type grindingapparatus to an average size of 10-15 microns in length, according tothe usual commercial procedure.

These data show that the composition of Example 1 dissolvedapproximately twice as rapidly as did the standard sample of fluorescentWhitening agent. The sample also showed approximately 25 percentstronger dyeing of cotton cloths after 5 and 10 minute washing cyclesthan did the standard sample of fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 1 wereprepared and were measured for color grade on a Hunterlab Model D25Color and Color-Difference Meter (Hunter Associates Laboratory, lnc.,Fairfax, Virginia), in accordance with the general method described inthe Journal of the Optical Society of America, 48, 985 (1958). Theabovedescribed composition was found to be within the range of colorspecifications required for use in detergent powders and desirably muchwhiter, pinker and bluer than the standard sample of fluorescentwhitening agent which had been ground to equivalent particle size in theabsence of sodium sulfate.

EXAMPLE 2 A laboratory blender (Kitchenaid Model KS-A manufactured bythe Hobart Mfg. Co., Troy, Ohio) was charged with a 700 g presscake ofdisodium 4,4'-bis(4-anilino-o-morpholino-s-triazin-Z-ylamino)-2,2'-stilbenedisulfonatecontaining 68.8 percent solids [481g of fluorescent whitening agent and219 g (12.2 moles) of water]. Anhydrous sodium sulfate (481 g; 3.39moles) was added, while mixing was continuously maintained at roomtemperature. After approximately ten minutes, mixing was stopped and thepowder-like mixture was passed through a two-roll mill at roomtemperature. The two-roll mill (manufactured by Reliable Rubber andPlastic Equipt. Mfg. Co., North Bergen, New Jersey) having two rolls sixinches in diameter and thirteen inches in length, which rotate in aratio of approximately 1:1.25, was set to exert separating forces in therange of 1,000 to 2,000 pounds per linear inch. The milled mixture wasthen dried in an oven at l05l 10C to a constant weight and was finallypassed through a pulverizing machine (Mikro Pulverizer Type CF,manufactured by Pulverizing Machinery Div., Metals Disintegrating Inc.,Summit, N.J.). The fine granular powder thus obtained containedapproximately 51 percent of disodium4,4'-bis-(4-anilino-6-morpholinos-triazin-2-ylamino)-2,2'-stilbenedisulfonateand approximately 49 percent of anhydrous sodium sulfate. Examination ofthis product under the microscope showed that the fluorescent whiteningagent existed as broken crystals averaging 3 microns with substantiallyno crystals greater than 15 microns in their largest dimension.

The rate of solution of the above-described composition in water-wasdetermined by following the same procedure described in Example 1 above.

Sample Temp. F 7( Dissolved Time (min) Example 2 5 do. do. 97 7 do. do.100 l 1 Standard 80 90 23 do. do. 97 28 do. do. 100 3-1.5

These data show that the composition of Example 2 dissolved inapproximately one-third the amount of time as did the standard sample offluorescent whiten ing agent. This sample also exhibited approximately25 percent stronger dyeing of cotton cloths after five and ten minutewashing cycles than did the standard sample of fluorescent whiteningagent.

Detergent compositions incorporating the composition of Example 2 wereprepared and measured for color grade in accordance with the testprocedure described in Example 1. The composition of Example 2 was foundto be within the range of color specifications required for use indetergent powders and was found desirably to be much whiter, pinker andbluer than the standard sample of fluorescent whitening agent which hadbeen ground to equivalent particle size in the absence of sodiumsulfate.

EXAMPLE 3 Four thousand pounds of dried presscake consisting ofcrystalline disodium 4,4'-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate having anaverage particle size of approximately X l5 microns was charged into aribbon-blender together with 4,000 pounds of anhydrous sodium sulfate.The mixture was blended for 30 minutes and was then subjected togrinding in a Model No. 0304 Jet-O-Mizer Mill (a fluid energy attritionapparatus manufactured and supplied by the Fluid Energy Processing andEquipment Co., Lausdale, Pa.) using predried compressed air at atemperature of approximately 50C at the mill. The mill was operated at amill nozzle pressure of 100 pounds per square inch and a feed nozzlepressure of 90 pounds per square inch. The blended composition waspassed through the mill at a rate of approximately 1000 pounds per hour.The fine granular powder thus obtained contained approximately 50 percent of disodium4,4'-bis(4-anilino-o-morpholino-striazin-2-ylamino)-2,2-stilbenedisulf0nateand approximately 50 percent anhydrous sodium sulfate. Microscopicexamination showed that the fluorescent whitening agent existed asbroken crystals averaging 5 microns with substantially none of thecrystals greater than microns in their largest dimension.

The above-described composition was found to have essentially the samerates of solution as those found for the composition of Example 2 aboveand was also found to exhibit approximately percent stronger dyeing ofcottom cloths after 5 and 10 minute washing cycles than did the standardsample of fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 3 wereprepared and measured for color grade in accordance with the testprocedure described in Example I. The composition of Example 3 was foundto be within the range of color specifications required for use indetergent powders and was found desirably to be much whiter, pinker andbluer than the standard sample of fluorescent whitening agent which hadbeen ground to equivalent particle size in the absence of sodiumsulfate.

I claim:

1. A process for treating a presscake consisting essentially of waterand relatively large crystals of a fluorescent whitening agent selectedfrom the group consisting of disodium4,4-bis-(4,6-dianilino-s-triazin-2- ylamino)-2,2-stilbenedisulfonate,disodium 4,4-'bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2.2-stilbenedisulfonate,disodium 4,4-bis(4-anilino-6-[2,2'-dihydroxyethylamino]-s-triazin-2-ylamino)-2,2-stilbenedisulfonate,disodium 4,4-bis(4-anilino-6-[2hydroxyethylamino]-s-triazin-2-ylamino)-2,2-stilbenedisulfonate andsodium 2-(4-stilbyl)-naphtho-[l, 2':4,5]-l,2,3-triazole-2-sulfonate,which comprises grinding said presscake at a temperature of 20 to 60C inthe presence of at least one and up to eight molecular equivalents ofanhydrous sodium sulfate for each ten molecular equivalents of water insaid prcsseake until the crystals are reduced to an average particlesize of approximately 5 microns with substantially none of the crystalsgreater than 15 microns in the largest dimension.

2. A process according to claim 1 wherein the fluorescent whiteningagent is disodium 4,4-bis(4-anilino- 6m0rpholino-s-triazin-Z-ylamino)-2,2-stilbenedisulfonate.

3. A process according to claim 1 wherein the grinding is accomplishedin the presence of approximately one molecular equivalent of anhydroussodium sulfate for each 10 molecular equivalents ofwater in thepresscake.

4. A process according to claim 3 wherein the fluorescent whiteningagent is disodium 4,4'-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)2,2-stilbenedisulfonate.

5. A process according to claim 1 with the additional step whichcomprises drying the product obtained in accordance with claim 1 toremove some or all of the moisture content.

6. A process according to claim 5 wherein the fluorescent whiteningagent is disodium 4,4'-bis(4-anilino--morpholino-s-triazin-2-ylamino)-2,2'-stilbenedusulfonate.

7. A process for treating a presscake consisting essen' tially ofrelatively large crystals of a fluorescent whitening agent selected fromthe group consisting of disodium4,4'-bis(4,6-dianilino-s-triazin-2-ylamino)-2,2'- stilbenedisulfonate,disodium 4,4'-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate, disodium4,4-bis(4-anilino-6-[2,2'-dihydroxyethylamino]-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate,disodium 4,4-bis(4-anilino-6-[2-hydroxyethylamino]-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate andsodium 2-(4- stilbyl)naphtho[ l ,2:4,5]-1,2,3-triazole-2-sulfonate,which comprises grinding said presscake in the presence of approximately30 to approximately 65 percent of anhydrous sodium sulfate by weight ofthe resultant mixture until the crystals are reduced to an averageparticle size of approximately 5 microns with substantially none of thecrystals greater than 15 microns in the largest dimension.

8. A process according to claim 7 wherein the fluorescent whiteningagent is disodium 4,4'-bis(4-anilino-6-morpholino-s-triazin-Z-ylamino)-2,2'-stilbenedisulfonate.

1. A PROCESS FOR TREATING A PRESSCAKE CONSISTING ESSENTIALLY OF WATERAND RELATIVELY LARGE CRYSTALS OF A FLUOROSCENT WITHENTING AGENT SELECTEDFROM THE GROUP CONSISTING OF DISODIUM4,4''-BIS(4,6-DIANILINO-S-TRAZIN-2-YLAMINO)-2,2''-STIBENEDISULFONATE,DISODIUM4,4''-BIS(4-ANILINO-6-MORPHOLINO-S-TRIAZIN-2YLAMINO)-2,2''-STILBENEDISULFONATE,DISODIUM4,4''-BIS(4-ANILINO6-(2.2''-DIHYDROXYETHYLAMINO)-S-TRIAZIN-2-YLAMINO)-2,2''STILBENEDISULFONATE, DISODIUM4,''-BIS(4-ANILINO-6-(2HYDROXYETHYLAMINO)-S-TRIAZIN-2-YLAMINO)-2,2''STILBENEDISULFONATE AND SODIUM 2-(4-STILBYL)-NAPHTHO-(1'',2''-:4,5)-1,2,3-TRIAZOLE-2-SULFONATE, WHICH COMPRISES GRINDING SAIDPRESSCAKE AT A TEMPERATURE OF 20* TO 60*C IN THE PRESENCE OF AT LEASTONE AND UP TO EIGHT MOLECULAR EQUIVALENTS OF ANHYDROUS SODIUM SULFATEFOR EACH TEN MOLECULAR EQUIVALENTS OF WATER IN SAID PRESSCAKE UNTIL THECRYSTALS ARE REDUCED TO AN AVERAGE PARTICLE SIZE OF APPROXIMATELY 5MICRONS WITH SUBSTANTIALLY NONE OF THE CRYSTALS GREATER THAN 15 MICRONSIN THE LARGEST DIMENSION.
 1. A process for treating a presscakeconsisting essentially of water and relatively large crystals of afluorescent whitening agent selected from the group consisting ofdisodium 4,4''-bis-(4,6-dianilino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium4,4''-bis(4-anilino-6-(2,2''-dihydroxyethylamino)-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium4,4''-bis(4-anilino-6-(2-hydroxyethylamino)-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate and sodium 2-(4-stilbyl)-naphtho-(1'',2'':4,5)-1,2,3-triazole-2-sulfonate, which comprises grinding saidpresscake at a temperature of 20* to 60*C in the presence of at leastone and up to eight molecular equivalents of anhydrous sodium sulfatefor each ten molecular equivalents of water in said presscake until thecrystals are reduced to an average particle size of approximately 5microns with substantially none of the crystals greater than 15 micronsin the largest dimension.
 2. A process according to claim 1 wherein thefluorescent whitening agent is disodium4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate.
 3. A process according to claim 1 wherein thegrinding is accomplished in the presence of approximately one molecularequivalent of anhydrous sodium sulfate for each 10 molecular equivalentsof water in the presscake.
 4. A process according to claim 3 wherein thefluorescent whitening agent is disodium4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate.
 5. A process according to claim 1 with theadditional step which comprises drying the product obtained inaccordance with claim 1 to remove some or all of the moisture content.6. A process according to claim 5 wherein the fluorescent whiteningagent is disodium4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2''-stilbenedusulfonate.
 7. A process for treating a presscake consistingessentially of relatively large crystals of a fluorescent whiteningagent selected from the group consisting of disodium4,4''-bis(4,6-dianilino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate,disodium 4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium4,4''-bis(4-anilino-6-(2,2''-dihydroxyethylamino)-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium4,4''-bis(4-anilino-6-(2-hydroxyethylamino)-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate and sodium2-(4-stilbyl)naphtho(1'',2'':4,5)-1,2,3-triazole-2-sulfonate, whichcomprises grinding said presscake in the presence of approximately 30 toapproximately 65 percent of anhydrous sodium sulfate by weight of theresultant mixture until the crystals are reduced to an average particlesize of approximately 5 microns with substantially none of the crystalsgreater than 15 microns in the largest dimension.